The unique promise put forth in your Dominant Selling Idea has to matter more to your prospect than any other promise you or your competitors can make for it to be either dominant or a selling idea. It has to have a direct, obvious impact on either pain or desire. As simple as it may sound, customers have to want it.
Massive numbers of Harvard and Stanford MBAs lost a billions of dollars of investor capital by ignoring this Granite Page, which is also the second ingredient for a Dominant Selling Idea. They built dot-com businesses around concepts that were brilliants in every respect except one: people didn't want the product. In other words, the idea wasn't important to prospect.
So you may proclaim to the world that your store has the world's largest selection of brown ties. But if prospects don't care about brown ties, you'll need another Dominant Selling Idea.